public class LoopQueue<E> implements Queue<E> {
    private E[] data;
    private int front,tail;
    private int size;

    public LoopQueue(int capacity){
        //循环队列会浪费一个空间
        data = (E[])new Object[capacity+1];
        front = 0;
        tail = 0;
        size = 0;
    }

    public LoopQueue(){
        this(10);
    }

    public int getCapacity(){
        return data.length-1;
    }

    @Override
    public boolean isEmpty(){
        return front==tail;
    }

    @Override
    public int getSize(){
        return size;
    }

    @Override
    public void enqueue(E e){
        if((tail+1)% data.length ==front){
            resize(getCapacity()*2);
        }
        data[tail] = e;
        tail = (tail+1)%data.length;
        size++;
    }

    @Override
    public E dequeue(){
        if(isEmpty()){
            throw new IllegalArgumentException("Cannot dequeue an empty queue");
        }
        E ret = data[front];
        data[front] = null;
        front  =(front+1)%data.length;
        size--;
        if(size == getCapacity()/4 && getCapacity()/2 != 0){
            resize(getCapacity()/2);
        }
        return ret;
    }

    @Override
    public E getFront(){
        if(isEmpty()){
            throw new IllegalArgumentException("Queue is empty");
        }
        return data[front];
    }

    private void resize(int newCapacity){
        E[] newData = (E[])new Object[newCapacity+1];
        for (int i = 0; i < size; i++) {
            newData[i] = data[(front+i)%data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append(String.format("Queue:size = %d,capacity = %d\n",size,getCapacity()));
        res.append("front [");
        for (int i = front; i != tail; i=(i+1)%data.length) {
            res.append(data[i]);
            if((i+1)%data.length != tail){
                res.append(", ");
            }
        }
        res.append("] tail");
        return res.toString();
    }
}
